(19)

(11)

EP 0 138 898 A1

(12)

(43) Date of publication: 02.05.1985 Bulletin 1985/18 (21) Application number: 84901205.0 (22) Date of filing: 15.03.1984

(51) International Patent Classification (IPC):  H01J 49/ 42( . ) (86) International application number: PCT/GB1984/000080 (87) International publication number: WO 1984/003994 (11.10.1984 Gazette 1984/24)

(84) Designated Contracting States: AT BE CH DE FR GB LI LU NL SE (30) Priority: 28.03.1983 GB 19830008445 (71) Applicant: PRUTEC LIMITED London EC1N 2NH (GB)	(72) Inventor: OTTLEY, Thomas, William Herts SG8 5QM (GB)